The mechanisms whereby the catecholamine content of carotid bodies is regulated by physioloic or pharmacologic stimuli was studied. Short-lasting exposure to hypoxia and stimulation of muscarinic receptors increases the rate of dopamine release without changing its turnover-rate. Neither the carotid sinus nor the sympathetic nerves participate in the modification of dopamine content by both types of stimuli. Injection of carbohydrate-active steroids causes a transient increase of dopamine content due to blockade of dopamine metabolism and a long-lasting increases in norepinephrine content which depended on an increased protein synthesis.